Usually, each first switching command comprises a change from a first value of the control signal to a second value of the control signal and requests the semiconductor power switch to be switched (e.g., turned on), and each second switching command comprises a change from the second value of the control signal to the first value of the control signal and requests the semiconductor power switch to be switched (e.g., turned off). The control signal generally is a digital signal in which the first and second value represent a logical zero and a logical one, respectively, or vice-versa.
The semiconductor power switch includes a voltage-controlled component such as an IGBT or a field-effect transistor. Although the semiconductor power switch may generally be either normally non-conductive or normally conductive if no voltage is applied to its control electrode, the following description focuses on normally non-conductive semiconductor power switches.
Many electronic power circuits include semiconductor switches that are nonconductive if no voltage is present at their control electrodes and become conductive when a control voltage is applied to their control electrodes (or vice-versa). Semiconductor power switches with insulated control electrodes (e.g., MOSFET or IGBT) normally operate at control voltages ranging from 10 to 15 volts.
If the semiconductor power switch is to become non-conductive, switching off the voltage applied to the control electrode may be sufficient in some applications. This is especially advantageous as only a single driver supply voltage is required. In many cases a simple bootstrap circuit may be used to supply this voltage.
In situations where the semiconductor power switch is operated in a bridge circuit (i.e., in a half or full bridge), it may however often be necessary to apply an inverted potential difference to its control electrode so that the power switch remains non-conductive even during transient processes. Integrated driver circuits currently available on the market are generally designed for operating voltages ranging from 15 to 20 volts. This may limit the maximum difference of the voltages that can be applied to the control electrodes.
If a higher difference of the voltages is needed to activate the semiconductor power switch, then the driver may in principle be designed using discrete and sufficiently voltage-proof components. Alternatively, the voltage can be converted to a higher level by means of a control voltage converter. Both solutions entail a significant amount of effort. The second solution is furthermore unsuitable for generating static voltages at the control electrode of the semiconductor power switch.
Published German Patent Application DE 37 18 001 A1 discloses a circuit arrangement configured to generate bipolar digital data signals from unipolar data signals which, in response to the unipolar data signals, connects a circuit output with the positive or negative terminal of a unipolar voltage source. To this end, the circuit arrangement features a switch combination implemented by inverters.
Published US Patent Application US 2004/0257155 A1 discloses an optically isolated bias control circuit that provides bias current for switching circuits, which may be used to control the switching of high power MOSFET-based switching circuits. The bias control circuit comprises a floating bias voltage source positive terminal electrically connected in series to the collector of a first photo-transistor. The emitter of the first photo-transistor is connected in series through an inductance to the parallel connected N-channel enhancement-mode MOSFET gate and to the collector of a second photo-transistor. The emitter of the second photo-transistor is connected to both the MOSFET source and to the negative terminal of the bias voltage source. Operation of this bias control circuit requires two complementary “ON” and “OFF” light signal pulses to be applied to the light sensitive base regions of the first and second photo-transistors, respectively. Minimal charge flow is achieved by allowing the active high “ON” light signal to be applied in the high state to the first photo-transistor only when the active high “OFF” light signal applied to the second photo-transistor is in the low state. This prevents the direct shorting of the bias voltage source through both photo-transistors and reduces the flow of charge required to control the MOSFET switching circuit. It is important to apply “ON” and “OFF” light signal pulses which have minimal rise and fall times to ensure that the MOSFET is driven as fast as possible through its switching states. The inductance in series with the gate is properly selected small to reduce switching losses by appropriately slowing the gate capacitor charging time. By using two additional optically isolating photo-transistors the polarity of the bias voltage source applied to the gate-to-source circuit of the MOSFET is effectively reversed in order to force the circuit off as fast as it is forced on.
There remains a need for a method of and a driver circuit for operating a semiconductor power switch having a control electrode and a reference electrode in response to first and second switching commands included in a control signal, which allow for precisely clocking fast switching semiconductor power switches at even high frequencies.